Cast your mind back to the early summer of 1997. Bliss it was in that dawn to be a new Labour minister, but to be a chancellor at Number 11 was very heaven. Labour's relations with the City had an unprecedented warmth, with many impressed by the prudent Mr Brown's decision to give the Bank of England independence. The truce, at least with the more trenchant Square Milers, was over by July, when Gordon Brown made his first budget and abolished a tax break for pension funds. It was a stealth tax, bankers decided: evidence that Labour was the same as ever. One industry lobby group thundered that it was the "biggest attack on funded pension provision since the war".

This weekend, the Treasury released officials' projections from before the tax change of its likely consequences. Mandarins certainly foresaw the ensuing fuss, warning that pension funds would react with "clamour and public consternation...Ministers' postbags will be pretty full." Unsurprising perhaps, since the estimated cost would be over £3bn a year. The documents were sufficient excuse for the Conservatives to launch another attack on a chancellor preparing to become prime minister. It was, they declared, evidence that Mr Brown had been "conning the country".

Big words for such a little measure. After all, what the opposition have spent the last decade referring to as Gordon Brown's great pensions raid was simply the removal of an obscure benefit that allowed pension funds to claim back the tax on share dividends. Norman Lamont had already squeezed the credit so that it was worth no more than tuppence for every 10p dividend. No surprise then that civil servants thought "pension schemes should be able to cope with the change" and that, in many cases, employers would make good any shortfall. Even if we accept the pension funds' own verdict that the credit's abolition cost them £5bn a year, it is hardly much for a trillion-pound industry which can lose (or make) more than that on the markets in a week. No wonder that on July 2 1997, as the chancellor sat down the stock market actually rose. All this gives the lie to the idea that the 1997 budget was the key to our pensions' decline. True, it was unhelpful - but so was the widespread habit of the "pension holiday", with many firms holding off from paying into their workers' schemes during the stockmarket bull run. There are lots of reasons why so many workers are now so worried about how much they will have to live on during their retirement. But the two big ones are simply that we can expect to live longer, so our pensions will have to stretch further, and that interest rates have fallen, so our schemes are no longer earning as much. These are global forces and to keep harping on about the loss of a solitary tax break is like a passenger on the Titanic getting miffed about losing a card game: there are rather bigger issues to worry about.

What makes these documents more than a stroll down memory lane - a kind of actuarial I Love 1997 - are the lessons it provides for the resident of No 11 as he prepares to move next door. One is political and has to do with how the papers came out. It took two years for journalists to secure their release under the Freedom of Information Act and the Treasury tried repeatedly to block them. These memos may provide ammunition for Mr Brown's enemies but the secrecy only gives further potency.

The other lesson is one of policy. The abolition of dividend tax credits was meant as a spur to companies to think long-term: less about rewarding shareholders and more about investment. The files show officials were doubtful it would do this. Yet the chancellor ploughed on, making it a key measure in his inaugural budget. It was a statement as much as a policy, with one consequence highlighted and the rest ignored. As his fabled first hundred days loom, Mr Brown should beware setting policy just to make a point.